Recording medium

ABSTRACT

The present invention provides a recording medium comprising a substrate having a glossy coating thereon, wherein the glossy coating comprises a binder and first and second groups of particles, wherein: 
     (a) the first group comprises metal oxide particles, wherein the metal oxide particles are aggregates of smaller, primary particles, 
     (b) the mean diameter of the primary particles is less than about 100 nm, 
     (c) the mean diameter of the aggregates is from about 100 nm to about 500 nm, 
     (d) the mean diameter of the particles in the second group is less than about 50% of the mean diameter of the aggregates in the first group, and 
     (e) the ratio of particles in the first group to particles in the second group is from about 0.1:1 to about 10:1 by weight. 
     The glossy coating of the inventive recording medium has an excellent rate of liquid absorption, a relatively high liquid absorption capacity, excellent adhesiveness, and a non-brittle, crack-resistant, glossy surface. Also provided is a method of preparing a recording medium and a coating composition useful in the preparation of a recording medium.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application claims priority to provisional U.S. Pat. App.No. 60/091,468 filed on Jul. 1, 1998.

This application claims benefit of Provisional Appln. 60/091,468 filedJul. 1, 1998.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a recording medium, a method for thepreparation of a recording medium, and a coating composition useful inthe preparation of a recording medium.

BACKGROUND OF THE INVENTION

A surface coating is sometimes applied to a recording medium in order toimprove its printing properties. For example, the coating can improvethe appearance, ink absorption, and/or image smear resistance of themedium.

Surface coatings can be classified into two general categories—glossycoatings and non-glossy (matte or dull) coatings. Glossy coatings areoften desirable, as they are very smooth, and can impart a superior feeland a photograph-like quality to a recorded image.

A coating composition comprising a pigment such as a hydratedaluminosilicate (such as a kaolin clay), titanium dioxide, alumina,silica, or calcium carbonate can be used to make a glossy coating if thecomposition is applied by cast coating, wherein the composition is driedwhile contacting a polished metal cylinder or drum (e.g., a polishedchromium drum). A glossy pigment coating prepared in this manner isadvantageous not only for its gloss, but because the pigment can imparta relatively high rate and capacity of ink absorption to the coating aswell. However, the cast coating procedure is relatively slow and costly.

It is possible to make glossy pigment coatings using application methodswhich are cheaper and faster than cast coating (e.g., bar coating,air-knife coating, roll coating, etc., sometimes followed bycalendering), but the overall gloss of the resulting coating is oftendiminished compared to cast coating. Moreover, glossy pigment coatingsprepared using these rapid, inexpensive methods also can be quitebrittle, and the coatings often crack and flake upon drying.

Coating compositions comprising resins such as polyolefin resin,polyester resin, polyamide resin, or polycarbonate resin can be appliedusing the aforementioned rapid, inexpensive coating methods (e.g., barcoating, air-knife coating, roll coating, etc.), to form coatings havinga high gloss. However, a recording medium having such a glossy resincoating generally has significantly decreased rates of ink absorptionand ink drying compared to a recording medium having a pigment coating.

A need exists for a recording medium having a glossy coating that can beapplied using a rapid, inexpensive coating procedure, wherein the glossycoating is non-brittle, and wherein ink applied to the recording mediumis rapidly absorbed, and rapidly dries. A need also exists for a methodof preparing such a glossy recording medium, and for a coatingcomposition that can be used in such a method. The present inventionprovides such a recording medium, method, and composition.

BRIEF SUMMARY OF THE INVENTION

The recording medium of the present invention comprises a substratehaving a glossy coating thereon, wherein the glossy coating comprisesfirst and second groups of particles, wherein:

(a) the first group comprises metal oxide particles, wherein the metaloxide particles are aggregates of smaller, primary particles,

(b) the mean diameter of the primary particles is less than about 100nm,

(c) the mean diameter of the aggregates is from about 100 nm to about500 nm,

(d) the mean diameter of the particles in the second group is less thanabout 50% of the mean diameter of the aggregates in the first group, and

(e) the ratio of particles in the first group to particles in the secondgroup is from about 0.1:1 to about 10:1 by weight.

The coating composition of the present invention comprises a suitablecarrier and first and second groups of particles, has a solids contentof at least about 15% by weight, has an apparent viscosity at arelatively high shear rate of less than about 100 centipoise at 22° C.,and can be applied to a substrate to form a substrate having a glossycoating thereon.

The inventive method of preparing a recording medium comprises: (a)providing a substrate, (b) coating the substrate with the coatingcomposition of the present invention to provide a coated substrate, and(c) drying the coated substrate to form the recording medium.

The recording medium of the present invention comprises a substratehaving a glossy coating thereon, wherein the glossy coating isnon-brittle and crack-resistant, has an excellent rate of liquidabsorption, has a relatively high liquid absorption capacity, hasexcellent adhesiveness, and can be applied using rapid, inexpensivecoating methods. These and other advantages of the present invention, aswell as additional inventive features, will be apparent from thedescription of the invention provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the rheograms of two coating compositions of thepresent invention and the rheograms of two analogous coatingcompositions that utilize a single type of particle population.

FIG. 2 graphically depicts the change in contact angle over time(absorptivity of distilled water) for a recording medium of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a recording medium, a method for thepreparation of a recording medium, and a coating composition useful inthe preparation of a recording medium. It has surprisingly andunexpectedly been discovered that rapid, inexpensive coating methods canbe used to provide a substrate with a non-brittle, crack-resistant,adhesive, glossy coating, wherein the glossy coating has a relativelyrapid rate of liquid absorption, a relatively rapid rate of liquiddrying, and a relatively large liquid absorption capacity. The glossycoating comprises first and second groups of particles, wherein thefirst group comprises metal oxide particles that are aggregates ofsmaller primary particles, and the second group comprises particleshaving a mean diameter of less than about 50% of the mean diameter ofthe aggregates in the first group.

Recording Medium

The present invention provides a recording medium comprising a substratehaving a glossy coating thereon, wherein the glossy coating comprises abinder and first and second groups of particles, wherein:

(a) the first group comprises metal oxide particles, wherein the metaloxide particles are aggregates of smaller, primary particles,

(b) the mean diameter of the primary particles is less than about 100nm,

(c) the mean diameter of the aggregates is from about 100 nm to about500 nm,

(d) the mean diameter of the particles in the second group is less thanabout 50% of the mean diameter of the aggregates in the first group, and

(e) the ratio of particles in the first group to particles in the secondgroup is from about 0.1:1 to about 10:1 by weight.

The glossiness of a recording medium can be measured, for example, interms of the 75° specular gloss according to JIS P 8142, or anequivalent U.S. standard, using a gloss photometer (e.g., VGS-1001,manufactured by Nihon Denshoku Kogyosha), a Hunter 75° Gloss Meter, aTechnidyne Glossmeter (e.g., Model T480A), or the like. Any suitabletest method can be used to determine glossiness, for example, ASTM,TAPPI, or the like. When TAPPI is used, it is preferably TAPPI T480.When ASTM is used, it is preferably ASTM D1223. Desirably, the recordingmedium of the present invention is calendered to provide a glossiercoating. It is preferred that the recording medium of the presentinvention has a 75° specular gloss of at least about 15%. Morepreferably, the recording medium of the present invention has a 75°specular gloss of at least about 25%, even more preferably at leastabout 35%, and still more preferably at least about 45%, yet morepreferably at least about 55%, and most preferably at least about 65%.

When the substrate is a cellulose substrate (e.g., cellulose paper), therecording medium of the present invention, when calendered, preferablyhas a 75° specular gloss of at least about 15%, more preferably at leastabout 25%, even more preferably at least about 35%, and still morepreferably at least about 45%. In a preferred embodiment, the recordingmedium of the present invention, when calendered, has a 75° speculargloss of at least about 50%.

The inventive recording medium comprises a substrate, which can beeither transparent or opaque, and can comprise any suitable material.Examples of such materials include, but are not limited to, films orsheets of polyester resins (e.g., poly(ethylene terephthalate)),diacetate resins, triacetate resins, acrylic resins, polycarbonateresins, polyvinyl chloride resins, polyimide resins, cellophane andcelluloid, glass sheets, metal sheets, plastic sheets, paper (e.g.,cellulose paper), coated paper (e.g., resin-coated paper),pigment-containing opaque films, and foamed films. Polyester sheets andcellulose paper are preferred, with poly(ethylene terephthalate) sheetsbeing more preferred.

The glossy coating can be applied to the substrate using any suitablemethod or combination of methods.

Preferably, the substrate is coated with a coating compositioncomprising a binder, a suitable carrier (e.g., water), and first andsecond groups of particles, wherein:

(a) the first group comprises metal oxide particles, wherein the metaloxide particles are aggregates of smaller, primary particles,

(b) the mean diameter of the primary particles is less than about 100nm,

(c) the mean diameter of the aggregates is from about 100 nm to about500 nm,

(d) the mean diameter of the particles in the second group is less thanabout 50% of the mean diameter of the aggregates in the first group, and

(e) the ratio of particles in the first group to particles in the secondgroup is from about 0.1:1 to about 10:1 by weight, to provide a coatedsubstrate. After applying the coating, the coated substrate is driedusing any suitable method or combination of methods to provide therecording medium of the present invention, which can optionally becalendered to improve its glossiness.

The coating composition can be applied using any suitable method orcombination of methods. Suitable methods include, but are not limitedto, roll coating, blade coating, air knife coating, rod coating, barcoating, cast coating, gate roll coating, wire bar coating, short-dowelcoating, slide hopper coating, curtain coating, flexographic coating,gravure coating, Komma coating, size press coating in the manner of on-or off-machine, and die coating, with rapid, inexpensive methods such asrod coating and air knife coating being preferred.

Suitable drying methods include, but are not limited to, air orconvection drying (e.g., linear tunnel drying, arch drying, air-loopdrying, sine curve air float drying, etc.), contact or conductiondrying, and radiant-energy drying (e.g., infrared drying and microwavedrying).

The glossy coating can be of any suitable thickness. In particular, thecoating is preferably from about 1 μm to about 50 μm in thickness, morepreferably from about 5 μm to about 30 μm in thickness, and mostpreferably from about 10 μm to about 20 μm in thickness.

The recording medium of the present invention can comprise a substratehaving more than one coating layer, which can be the same or different,provided that at least one of the coating layers comprises first andsecond groups of particles, wherein:

(a) the first group comprises metal oxide particles, wherein the metaloxide particles are aggregates of smaller, primary particles,

(b) the mean diameter of the primary particles is less than about 100nm,

(c) the mean diameter of the aggregate particles is from about 100 nm toabout 500 nm,

(d) the mean diameter of the particles in the second group is less thanabout 50% of the mean diameter of the aggregates in the first group, and

(e) the ratio of particles in the first group to particles in the secondgroup is from about 0.1:1 to about 10:1 by weight. For example, therecording medium of the present invention can comprise a substratecoated with one or more ink-receptive layers (e.g., comprising kaolinclay) and/or one or more resin-containing layers (e.g., a glossy,laminated film layer). Although the recording medium of the presentinvention can comprise coatings in addition to a coating comprisingfirst and second groups of particles as described above (e.g.,ink-receptive layers, glossy layers, etc.), it has surprisingly andunexpectedly been found that the above-described coating comprisingfirst and second groups of particles provides sufficient ink receptivityand gloss for the vast majority of printing applications.

The first group (population) of particles is primarily responsible forthe liquid absorption characteristics of the glossy coating. The firstgroup preferably comprises particles of one or more metal oxides such assilica, alumina, titania, zirconia, ceria, and magnesia, with pyrogenicmetal oxides and finely milled metal oxide gels being preferred,pyrogenic metal oxides being especially preferred, and pyrogenic silicabeing most preferred. The metal oxide can be charged or uncharged, andif charged, can be cationic, anionic, or amphoteric. It is sometimespreferred that cationic particles be included in the glossy coating.Although many metal oxides are either neutral or anionic, they can bemade cationic via surface modification. For example, silica, which isanionic, can be made cationic by treating the silica with one or moreinorganic cationic modifiers, for example, an inorganic salt (e.g.,aluminum chlorohydrate), or the like. Likewise, silica can be madecationic by treating the silica with one or more organic cationicmodifiers, for example, a silane, a polymer (e.g., a polyamine polymer),or the like.

The first group preferably comprises metal oxide particles, which areaggregates of smaller, primary particles. Because the surface area of aprimary particle is inversely proportional to its size, and because ahigh surface area has a beneficial effect on many properties of theglossy coating (e.g., rate of liquid absorption and liquid absorptioncapacity), it is preferred that the primary particles have a meandiameter of less than about 100 nm (e.g., from about 1 nm to about 100nm). More preferably, the first group comprises aggregates of primaryparticles, wherein the primary particles have a mean diameter of lessthan about 50 nm (e.g, from about 1 nm to about 50 nm), even morepreferably less than about 30 nm (e.g., from about 1 nm to about 30 nm),yet more preferably less than about 20 nm (e.g, from about 1 nm to about20 nm), and most preferably less than about 15 nm (e.g., from about 1 nmto about 15 nm). It is highly preferred that substantially all of theprimary particles have diameters smaller than the mean diameter valuesset forth above. In other words, it is highly preferred thatsubstantially all of the primary particles have diameters of less thanabout 100 nm (e.g., from about 1 nm to about 100 nm), more highlypreferred that substantially all of the primary particles have diametersof less than about 50 nm (e.g., from about 1 nm to about 50 nm), evenmore highly preferred that substantially all of the primary particleshave diameters of less than about 30 nm (e.g., from about 1 nm to about30 nm), yet more highly preferred that substantially all of the primaryparticles have diameters of less than about 20 nm (e.g., from about 1 nmto about 20 nm), and most highly preferred that substantially all of theprimary particles have diameters of less than about 15 nm (e.g., fromabout 1 nm to about 15 nm).

A metal oxide particle that is an aggregate of smaller primaryparticles, such as a pyrogenic metal oxide, has a porous substructure,and coatings that comprise such particles have a relatively rapid rateof liquid absorption, and a relatively high liquid absorption capacity.The rate of liquid absorption can be measured, for example, by applyinga droplet of a liquid (e.g., distilled water) to the coating surface andmeasuring the change in the angle of the droplet with respect to thesurface (contact angle) over time. Preferably, the contact angle ofdistilled water, when applied to the glossy coating of the recordingmedium of the present invention, decreases by at least about 5° over thefirst five minutes. More preferably, the contact angle decreases by atleast about 7° over the first five minutes. Most preferably, the contactangle of distilled water, when applied to the glossy coating of therecording medium of the present invention, decreases by at least about10° over the first five minutes.

The capacity of liquid absorption can be measured by contacting aliquid, for example, water, or a 1:1 solution of polyethylene glycol(e.g., PEG 400) and water, or the like, with a predetermined area of theglossy coating of the recording medium of the present invention for 10seconds at 22° C., followed by contacting the medium with a blottingpaper to remove excess solution, measuring the weight of the solutionabsorbed by the glossy coating, and expressing that weight in terms ofg/m². Alternatively, the liquid absorption capacity of the coating canbe measured as a function of porosity. Porosity can be measured by anysuitable method, for example, by measuring the total intrusion volume ofa liquid (e.g., mercury) into the glossy coating applied to a non-poroussubstrate (e.g., polyethylene). It will be appreciated that the totalintrusion volume of a liquid for a particular coating (and, therefore,the porosity) can be a function of variables that influence thestructure of the coating, for example, binder type, pigment-to-binderratio, pigment particle size, calendering, and the like. Preferably, theporosity is determined by measuring the total intrusion volume ofmercury. The glossy coating of the recording medium of the presentinvention, when the substrate is a non-porous substrate, preferably hasa total mercury intrusion volume of at least about 0.3 cm^(3/)/g, morepreferably at least about 0.5 cm³/g, still more preferably at leastabout 0.8 cm³/g, most preferably about 1 cm³/g or greater. Liquidabsorptivity also can be measured by applying a droplet of a suitableliquid (e.g., distilled water) to the surface of the recording medium,and measuring the change in contact angle over time as described herein.

With respect to the mean diameter of the aggregate particles in thefirst group, it is preferred that the aggregates have a mean diameter(as measured by a light scattering technique, for example, using aBrookhaven 90Plus Particle Scanner, available from BrookhavenInstruments Corporation, Holtsville, N.Y., of less than about 500 nm(e.g, from about 70 or 100 nm to about 500 nm), more preferably lessthan about 400 nm (e.g., from about 70 or 100 nm to about 400 nm), evenmore preferably less than about 300 nm (e.g, from about 70 or 100 nm toabout 300 nm), and most preferably less than about 200 nm (e.g., fromabout 70 or 100 nm to about 200 nm (such as about 150 nm)). It ispreferred that substantially all of the aggregate particles havediameters smaller than the mean diameter values set forth above. It ishighly preferred that substantially all of the aggregates have diametersof less than about 1 μm (e.g., from about 70 or 100 nm to about 1 μm),more highly preferred that substantially all of the aggregates havediameters of less than about 500 nm (e.g., from about 70 or 100 nm toabout 500 nm), even more highly preferred that substantially all of theaggregates have diameters of less than about 400 nm (e.g., from about 70or 100 nm to about 400 nm), yet more highly preferred that substantiallyall of the aggregates have diameters of less than about 300 nm (e.g.,from about 70 or 100 nm to about 300 nm). Desirably, substantially allof the aggregates have mean diameters of less than about 200 nm (e.g.,from about 70 or 100 nm to about 200 nm).

The primary particles and/or aggregates in the first group can have arelatively wide or narrow range of individual particle diameters. Forinstance, the primary particles, aggregate particles, or both, can bemonodispersed. By monodispersed is meant that the particles havediameters that are substantially identical. For example, substantiallyall monodispersed 55 nm particles have diameters in the range of fromabout 50 nm to about 60 nm. It is preferred that the range of diametersof monodispersed particles be narrower (e.g., from about 53 to about 57nm for monodispersed 55 nm particles), and more preferred that the rangebe even narrower (e.g., from about 54 nm to about 56 nm formonodispersed 55 nm particles).

The coating comprises a second group (population) of particles inaddition to the first group of metal oxide particles. It is believedthat the particles in the second group, which have a mean diameter atleast about 50% smaller than the mean diameter of the aggregates in thefirst group, improve the packing of the metal oxide aggregates byfilling in the void space between the aggregate particles. This providesa more densely packed glossy coating, which is non-brittle, resistscracking, and is strongly adhesive. However, even though the particlesin the coating are densely packed, with minimal inter-particle voids,the coating retains a high porosity due to the intra-particle voids ofthe aggregate particles.

It has been found that the packing density of the glossy coating on therecording medium of the present invention is increased when the coatingcomprises first and second groups of particles, wherein the particles inthe second group have a smaller mean diameter than the aggregates in thefirst group. For example, the particles in the second group can have amean diameter of less than about 50% of the mean diameter of theaggregates in the first group. The particles in the second group alsocan have a mean diameter of less than about 40% of the mean diameter ofthe aggregates in the first group, or even less than about 30% (e.g.,less than about 20% of the mean diameter of the aggregates in the firstgroup). In some cases, it can be desirable for substantially all of theparticles in the second group to have mean diameter of less than about10% of the mean diameter of the aggregates in the first group.

Desirably, the particles in the second group have a mean diameter ofless than about 300 nm (e.g., from about 1 nm to about 300 nm).Typically, the particles in the second group have a mean diameter ofless than about 200 nm (e.g, from about 1 nm to about 200 nm).Preferably, the particles in the second group have a mean diameter ofless than about 100 nm (e.g., from about 1 nm to about 100 nm), morepreferably, less than about 50 nm (e.g, from about 1 nm to about 50 nm),even more preferably about 35 nm or less (e.g., from about 1 nm to about35 nm). In a particularly preferred embodiment, the mean diameter of theparticles in the second group is from about 20 nm to about 35 nm. Insome cases, the mean diameter of the particles in the second group caneven be less than about 20 nm (e.g., from about 1 nm to about 20 nm).

Although particles having a broad range of individual diameters can beused in the second group, it is preferred that substantially all of theparticles in the second group have diameters that are smaller than themean diameter of the aggregates in the first group. In particular, it ispreferred that substantially all of the particles in the second grouphave diameters of less than about 50% of the mean diameter of theaggregates in the first group. It is more preferred that substantiallyall of the particles in the second group have diameters of less thanabout 40% of the mean diameter of the aggregates in the first group.More preferably, substantially all of the particles in the second grouphave diameters of less than about 30% of the mean diameter of theaggregates in the first group. Even more preferably, substantially allof the particles in the second group can have diameters of less thanabout 20% of the mean diameter of the aggregates in the first group. Insome cases, it may be desirable for substantially all of the particlesin the second group to have diameters of less than about 10% of the meandiameter of the aggregates in the first group.

It is highly preferred that substantially all of the particles in thesecond group have diameters that are smaller than the diameters ofsubstantially all of the aggregates in the first group. In particular,it is highly preferred that substantially all of the particles in thesecond group have diameters of less than about 50% of the diameters ofsubstantially all of the aggregates in the first group. It is morepreferred that substantially all of the particles in the second grouphave diameters of less than about 40% of the diameters of substantiallyall of the aggregates in the first group. For example, substantially allof the particles in the second group can have diameters of less thanabout 30% of the diameters of substantially all of the aggregates in thefirst group. Desirably, substantially all of the particles in the secondgroup have diameters of less than about 20% of the diameters ofsubstantially all of the aggregates in the first group. In some cases,it may be desirable for substantially all of the particles in the secondgroup to have diameters of less than about 10% of the diameters ofsubstantially all of the aggregates in the first group.

More particularly, it is preferred that substantially all of theparticles in the second group have diameters of less than about 300 nm(e.g., from about 1 nm to about 300 nm), more highly preferred thatsubstantially all of the particles in the second group have diameters ofless than about 200 nm (e.g., from about 1 nm to about 200 nm), evenmore highly preferred that substantially all of the particles in thesecond group have diameters of less than about 100 nm (e.g., from about1 nm to about 100 nm), and most highly preferred that substantially allof the particles in the second group have diameters of less than about50 nm (e.g., from about 1 nm to about 50 nm).

Particles having a very narrow range of individual diameters, such asmonodispersed particles, also can be used in the second group.

The second group of particles also can comprise two or more portions ofparticles. If the second group of particles comprises two or moreportions of particles, it is preferred that each portion accounts for atleast about 1% by weight of the total particles in the second group. Itis more preferred that each portion accounts for at least about 5% byweight of the total particles in the second group, and most preferredthat each portion accounts for at least about 10% by weight of the totalparticles in the second group. Each portion can comprise particles ofdiffering materials (vide infra), differing mean diameters, and/ordiffering diameter ranges. For example, zero, one, two or more portionsof monodispersed particles can be used in the second group. If two ormore portions of monodispersed particles are used, it is preferred thatthe portions have unique (i.e., different) mean diameters. For example,the particles in the second group in a given glossy coating can comprise20% by weight of a portion of alumina particles having a mean diameterof about 150 nm, 30% by weight of a portion of monodispersed polystyrenelatex beads having a mean diameter of 55 nm, and 50% by weight of aportion of monodispersed colloidal silica particles with a mean diameterof 35 nm.

The particles in the second group can be charged or uncharged, and ifcharged, can be cationic, anionic, or amphoteric. It is sometimespreferred that cationic particles be included in the glossy coating.Although many metal oxides are either neutral or anionic, they can bemade cationic via surface modification. For example, silica, which isanionic, can be made cationic by treating the silica with a cationicmodifier such as an inorganic cationic modifier or an organic cationicmodifier as described herein.

The particles in the second group can comprise any suitable materials,such as metal oxides and synthetic polymers. Examples of suitablematerials include silica (e.g., colloidal or pyrogenic silica), alumina(e.g., alumina sols, colloidal alumina, cationic aluminum oxide orhydrates thereof, pseudoboehmite, etc.), surface-treated cationiccolloidal or pyrogenic silica, magnesium silicate, aluminum silicate,magnesium carbonate, calcium carbonate, kaolin, talc, calcium sulfate,barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinccarbonate, satin white, aluminum silicate, diatomaceous earth, calciumsilicate, aluminum hydroxide, lithopone, zeolite, hydrated halloycite,magnesium hydroxide, polyolefins (e.g., polystyrene, polyethylene,polypropylene, etc.), plastics (e.g., acrylic), urea resin, and melamineresin, with silica and polyolefins being preferred, and colloidal silicaand polystyrene being highly preferred.

Many physical properties of the glossy coating on the recording mediumof the present invention can be rationally optimized by varying therelative quantity of particles from each group contained therein.Although the particles in the second group can be porous, the porousmetal oxide aggregates of the first group will typically have a greaterimpact on the resulting liquid absorption characteristics of the coating(e.g., rate of absorption and absorption capacity). Thus, if a recordingmedium comprising a substrate with a highly absorptive glossy coating isdesired, the relative quantity of particles from the first group can beincreased, and the relative quantity of particles from the second groupdecreased. On the other hand, if a recording medium comprising asubstrate with a highly durable, crack-resistant, non-brittle, adherentglossy coating is desired, the relative quantity of particles from thefirst group can be decreased, and the relative quantity of particlesfrom the second group increased. In particular, it is preferred that therecording medium of the present invention comprise a coated substrate,wherein the coating comprises a ratio of particles from the first groupto particles in the second group (all portions) of from about 0.1:1 toabout 10:1 by weight, it is more preferred that the ratio of particlesfrom the first group to the second group be from about 0.2:1 to about8:1 by weight, even more preferably from about 0.3:1 to about 7:1 byweight, still more preferably from about 0.4:1 to about 6:1 by weight,yet more preferably from about 0.5:1 to about 5:1 by weight, and mostpreferably from about 0.6:1 to about 4:1 by weight (e.g., from about 1:1to about 3:1 by weight). In a particularly preferred embodiment, theratio of the particles from the first group to the second group is about4:1 by weight.

The recording medium of the present invention preferably comprises asubstrate coated with a coating comprising one or more binders, whichserve to bind the particles in the first and second groups to eachother, and to the substrate. If one or more binders are used, therelative ratio of the total particles in the first and second groups tothe total amount of binder(s) is preferably from about 1:1 to about 10:1by weight, more preferably from about 1.5:1 to about 8:1 by weight(e.g., from about 1.5:1 to about 5:1 by weight), even more preferablyfrom about 2:1 to about 6:1 by weight, and most preferably from about2:1 to about 4:1 or 5:1 by weight (e.g., about 3:1 by weight). Preferredbinders include, but are not limited to, polyvinyl alcohol (PVOH),polyvinyl acetate, polyvinyl acetal, polyvinyl pyrrolidone, oxidizedstarch, etherified starch, cellulose derivatives (e.g., carboxymethylcellulose (CMC), hydroxyethyl cellulose, etc.), casein, gelatin, soybeanprotein, silyl-modified polyvinyl alcohol, conjugated diene copolymerlatexes (e.g., maleic anhydride resin, styrene-butadiene copolymer,methyl methacrylate-butadiene copolymers, etc.), acrylic polymer latexes(e.g., polymers and copolymers of acrylic esters and methacrylic esters,polymers and copolymers of acrylic acid and methacrylic acid, etc.),vinyl polymer latexes (e.g., ethylene-vinyl acetate copolymer),functional group-modified polymer latexes obtained by modifying theabove-mentioned various polymers with monomers containing functionalgroups (e.g., carboxyl groups), aqueous binders such as thermosettingresins (e.g., melamine resin, urea resin, etc.), synthetic resin binderssuch as polymethyl methacrylate, polyurethane resin, polyester resin(e.g., unsaturated polyester resin), amide resin, vinyl chloride-vinylacetate copolymer, polyvinyl butyral, and alkyd resin, with polyvinylalcohol being most preferred.

It has been found that the glossy coating comprising first and secondgroups of particles exhibits a high degree of adhesiveness, both betweenthe particles themselves and between the particles and the substrate ofthe recording medium of the present invention. The adhesiveness isexemplified by both an increased crack-resistance of the dry, glossycoating, and an increase in pick strength. The crack resistance of thecoating can be qualitatively measured by visual inspection, and the pickstrength can be quantified according to TAPPI T 499 and TAPPI UM 507.

The glossy coating of the recording medium of the present invention alsocan comprise one or more other additives, such as surfactants (e.g.,cationic surfactants, anionic surfactants such as long-chainalkylbenzene sulfonate salts and long-chain, preferably branched chain,alkylsulfosuccinate esters, nonionic surfactants such as polyalkyleneoxide ethers of long-chain, preferably branched-chain alkylgroup-containing phenols and polyalkylene oxide ethers of long-chainalkyl alcohols, and fluorinated surfactants), silane coupling agents(e.g., γ-aminopropyltrimethoxysilane, N-β (aminoethyl)γ-aminopropyltrimethoxysilane, etc.), hardeners (e.g., active halogencompounds, vinylsulfone compounds, aziridine compounds, epoxy compounds,acryloyl compounds isocyanate compounds, etc.), pigment dispersants,thickeners (e.g., carboxymethyl cellulose (CMC)), flowability improvers,antifoamers (e.g., octyl alcohol, silicone-based antifoamers, etc.),foam inhibitors, releasing agents, foaming agents, pentetrants, coloringdyes, coloring pigments, whiteners (e.g., fluorescent whiteners),preservatives (e.g., p-hydroxybenzoate ester compounds,benzisothiazolone compounds, isothiazolone compounds, etc.), antifungalagents, yellowing inhibitors (e.g., sodium hydroxymethanesulfonate,sodium p-toluenesulfinate, etc.), ultraviolet absorbers (e.g.,benzotriazole compounds having a hydroxy-dialkylphenyl group at the2-position), antioxidants (e.g., sterically hindered phenol compounds),antistatic agents, pH regulators (e.g., sodium hydroxide, sodiumcarbonate, sulfuric acid, hydrochloric acid, phosphoric acid, citricacid, etc.), water-resisting agents, wet strengthening agents, and drystrengthening agents.

The inventive recording medium has an excellent rate of liquid (e.g.,ink) absorption, a relatively high liquid absorption capacity, and adurable, rub-resistant, crack-resistant, glossy surface. Any suitableprinting method can be used to apply an image to the inventive recordingmedium. Such printing methods include, but are not limited to gravure,letterpress, collotype, lithography (e.g., offset lithography), ink-jet,and printing with hand-held implements (e.g., pens), with ink-jetprinting being preferred.

Coating Composition

The present invention also provides a coating composition that can beused to apply a glossy coating to a substrate. The inventive coatingcomposition has a solids content of at least about 15% by weight, anapparent viscosity at relatively high shear rate of less than about 100centipoise at 22° C., and comprises a suitable binder and first andsecond groups of particles, wherein:

(a) the first group comprises metal oxide particles, wherein the metaloxide particles are aggregates of smaller, primary particles,

(b) the mean diameter of the primary particles is less than about 100nm,

(c) the mean diameter of the aggregates is from about 100 nm to about500 nm,

(d) the mean diameter of the particles in the second group is less thanabout 50% of the mean diameter of the aggregates in the first group, and

(e) the ratio of particles in the first group to particles in the secondgroup is from about 0.1:1 to about 10:1 by weight.

The coating composition of the present invention typically includes asuitable carrier. The carrier can be any suitable fluid or combinationof fluids (e.g., solvents) in which the first and second groups ofparticles, and any other additives (e.g., one or more binders), can bemixed and applied to a substrate. Preferred carriers have a relativelyhigh vapor pressure to accelerate drying of the coating afterapplication, and preferred examples include, but are not limited to,organic solvents (e.g., methanol) and water, with water being mostpreferred.

The primary features of the coating composition of the present inventionare as previously described with respect to the recording medium of thepresent invention. For example, the properties of the first and secondgroups of particles (i.e., materials, diameters, relative quantities,etc.) are as previously described, and the properties of a glossycoating prepared using the inventive coating composition (i.e.,glossiness, rate and capacity of liquid absorption, packing density,adhesiveness, pick strength, crack resistance, etc.), and any additivescontained therein (e.g., surfactants, silane coupling agents, hardeners,etc.) are as previously described.

As previously described, many physical properties of a glossy coatingprepared with the coating composition of the present invention, can berationally optimized by varying the relative quantity of particles fromeach group contained therein. It will be appreciated that materialsother than the metal oxide particles (e.g., the binders, thickeners, andthe like) can be varied to alter or optimize the physical properties ofthe composition of the present invention.

It has been found that the ultimate physical properties of a glossycoating prepared with the inventive composition (e.g., rate of liquidabsorption, absorption capacity, brittleness, crack-resistance, etc.) isrelated to the coating structure. Some of the ultimate physicalproperties of the coating structure can be related to the apparentviscosity of the composition from which the coating is derived. In somecases, the coating structure can be related to the apparent viscosity ofthe coating composition from which the coating is derived. The relativequantity of particles from each of the first and second groups impactsthe apparent viscosity of the coating composition of the presentinvention. For some compositions, particularly those that have identicalcomponent particles, an increase in the quantity of particles from thesecond group relative to the first group, tends to exhibit a decrease inapparent viscosity, which can be related to an increase incrack-resistance of the dry, glossy coating.

The apparent viscosity of the coating composition of the presentinvention is, of course, also dependent on the solids content of thecomposition. It is sometimes preferred that the composition dryrelatively quickly to form a non-tacky glossy coating. In such cases, itis preferred that the solids content of the composition be high, and theamount of carrier be low. For the purposes of the present invention, itis preferred that the solids content of the inventive coatingcomposition be at least about 15% by weight, more preferred that thesolids content be at least about 20% by weight, and most preferred thatthe solids content be at least about 30% by weight. It will beappreciated that the apparent viscosity of the coating composition ofthe present invention also is a function of other factors, for example,shear rate. The coating composition of the present invention preferablyexhibits shear thinning to a degree which is desirable for a high-speedapplication characteristic of commercial coating processes. At arelatively high shear rate, for example, produced by a Hercules®High-Shear Viscometer at 4400 RPM (Bob: FF measuring geometry), theapparent viscosity can be below about 100 centipoise for a particularcomposition. The same composition can have a significantly higherapparent viscosity at a relatively low shear rate (e.g., as high as500-1200 centipoise when measured by a Brookfield Model RV viscometer at100 RPM, spindle #4, after 30 seconds).

It is preferred that the apparent viscosity of the inventive coatingcomposition be less than about 100 centipoise at about 22° C. at asolids content of about 15% by weight when measured in a Hercules®High-Shear Viscometer at 4400 rpm (Bob: FF measuring geometry), morepreferred that the apparent viscosity under these conditions be lessthan about 50 centipoise, even more preferably less than about 40centipoise, still more preferably less than about 30 centipoise, yetmore preferably less than about 20 centipoise, and most preferably lessthan about 10 centipoise at about 22° C. at a solids content of about15% by weight. Of course, other factors can influence the apparentviscosity of a coating composition having a particular solids content,for example, the pigment to binder ratio (ratio of dry particles to drybinder by weight).

When polyvinyl alcohol (PVOH) is used as a binder and the pigment tobinder ratio is 5:1, it is preferred that the apparent viscosity of thecoating composition of the present invention (without a thickener, asmeasured in a Hercules® High-Shear Viscometer at 4400 RPM (Bob: FFmeasuring geometry)) is less than about 100 centipoise at about 22° C.at a solids content of about 20% by weight. More preferably, theapparent viscosity of the coating composition of the present inventionunder these conditions is less than about 50 centipoise, even morepreferably less than about 40 centipoise, still more preferably lessthan about 30 centipoise, and most preferably less than about 20centipoise.

The coating composition of the present invention preferably comprisesone or more binders, which serve to bind the particles in the first andsecond groups to each other, and to the substrate to which thecomposition is applied. If one or more binders is used in the coatingcomposition of the present invention, the total amount of binder (i.e.,dry binder) is preferably from about 1% to about 50% of the composition(i.e., dry binder and particles combined) by weight. More preferably,the total amount of binder is from about 1% to about 40% of thecomposition by weight, even more preferably from about 1% to about 30%by weight, still more preferably from about 3% to about 25% by weight,yet more preferably from about 5% to about 15% by weight, and mostpreferably from about 5% to about 10% by weight (e.g., about 7% byweight). The ratio of the total particles in the first and secondgroups, to the total binder, is as previously described, as arepreferred binders.

When PVOH is used as a binder, the total amount of PVOH is preferablyfrom about 1% to about 50% of the composition by weight, more preferablyfrom about 1% to about 40% by weight, even more preferably from about 3%to about 40% by weight, yet more preferably from about 10% to about 30%by weight, and most preferably from about 20% to about 30% by weight.

The inventive coating composition can be used in any application whereina glossy coating having an excellent rate of liquid absorption, arelatively high liquid absorption capacity, and a durable,crack-resistant surface is desired. In a preferred use, the inventivecomposition can be applied to a substrate (e.g., paper or film) to forma glossy, ink absorptive layer on a recording medium. The coatingcomposition can be applied to a substrate using any suitable method orcombination of methods to form a glossy, ink absorptive coating.Suitable methods include, but are not limited to, roll coating, bladecoating, air knife coating, rod coating, bar coating, cast coating, gateroll coating, wire bar coating, short-dowel coating, slide hoppercoating, curtain coating, flexographic coating, gravure coating, Kommacoating, size press coating in the manner of on- or off-machine, and diecoating, with rapid, inexpensive methods such as rod coating and airknife coating being preferred. In a highly preferred application, aglossy, ink-absorptive coating is applied to a recording medium for usein ink-jet printing.

Method of Preparing a Recording Medium

The present invention also provides a method of preparing a recordingmedium. The inventive method of preparing a recording medium comprises:

(a) providing a substrate,

(b) coating the substrate with a coating composition to form substratehaving a glossy coating, wherein said coating composition has a solidscontent of at least about 15% by weight, an apparent viscosity (whenmeasured in a Hercules® High-Shear Viscometer at 4400 RPM (Bob: FFmeasuring geometry)) of less than about 100 centipoise at about 22° C.,and comprises a binder, a suitable carrier, and first and second groupsof particles, wherein:

(i) the first group comprises metal oxide particles, wherein the metaloxide particles are aggregates of smaller, primary particles,

(ii) the mean diameter of the primary particles is less than about 100nm,

(iii) the mean diameter of the aggregates is from about 100 nm to about500 nm,

(iv) the mean diameter of the particles in the second group is less thanabout 50% of the mean diameter of the aggregates in the first group,

(v) the ratio of particles in the first group to particles in the secondgroup is from about 0.1:1 to about 10:1 by weight, and

(c) drying the substrate having a glossy coating to form the recordingmedium. The recording medium also can optionally be calendered tofurther enhance gloss.

The primary features of the inventive method are as previously describedwith respect to the recording medium and coating composition of thepresent invention. For example, the preferred substrates, coatingmethods, coating composition (e.g., solids content, binder content,apparent density, additives, etc.), properties of the first and secondgroups of particles (i.e., materials, diameters, relative quantities,etc.), coating properties (i.e., thickness, number and constitution ofcoating layers, glossiness, rate and capacity of liquid absorption,packing density, adhesiveness, pick strength, crack resistance, etc.),are as previously described.

The coated substrate can be dried using any suitable method. Suitabledrying methods include, but are not limited to, air or convection drying(e.g., linear tunnel drying, arch drying, air-loop drying, sine curveair float drying, etc.), contact or conduction drying, andradiant-energy drying (e.g., infrared drying and microwave drying).

A glossy recording medium prepared according to the method of thepresent invention has an excellent rate of liquid (e.g., ink)absorption, a relatively high liquid absorption capacity, and a durable,rub-resistant, crack-resistant, glossy surface. Any suitable printingmethod can be used to apply an image to a recording medium preparedaccording to the present inventive method. Such printing methodsinclude, but are not limited to gravure, letterpress, collotype,lithography (e.g., offset lithography), ink-jet, and printing withhand-held implements (e.g., pens), with ink-jet printing beingpreferred.

The inventive recording medium, coating composition, and method for thepreparation of a recording medium can best be understood by reference tothe following examples. These examples further illustrate the presentinvention but, of course, should not be construed as in any way limitingits scope.

EXAMPLE 1

This example illustrates the preparation of a coating composition of thepresent invention. An initial aqueous silica slurry containing 25%solids was prepared. The solids in the initial slurry contained twodistinct populations of silica particles, which were 80% by weight PTGfumed silica (available from Cabot Corporation, Boston, Mass.) and 20%by weight LUDO™ colloidal silica (E.I. DuPont de Nemours, Wilmington,Del.). PTG is a fumed silica (surface area approximately 200 m²/g) whoseparticles are aggregates having a mean diameter of about 180 nm, asmeasured using a Brookhaven 90 Plus Particle Size Analyzer. Theaggregates of PTG are made up of smaller primary particles (meandiameter of about 12 nm as reported by the manufacturer). LUDOX™ is arelatively monodisperse substantially non-aggregated colloidal silicawhose particles have a mean diameter of 22 nm, as reported by themanufacturer.

A PVOH solution (prepared at 30% solids) was added to the initial silicaslurry at low agitation until the ratio of silica to PVOH (pigment tobinder ratio) was 5:1 by weight. The solids content of the compositionwas measured and water was added, if needed, until the final dispersionhad a total solids content (including PVOH) of 20%. The pH of the finaldispersion was 9.68. Thus formed was a coating composition of thepresent invention.

Comparative Example 1A

This example illustrates the preparation of a coating composition havingonly one type of population of particles. An initial aqueous silicaslurry of 30% solids content containing only PTG fumed silica (seeExample 1 for a description of PTG) was prepared. A PVOH solution(prepared at 30% solids) was added to the initial silica slurry at lowagitation until the ratio of silica to PVOH was 5:1 by weight. Thesolids content of the composition was measured and water was added, ifneeded, until the resulting dispersion had a total solids content(including PVOH) of 20%. The pH of the final dispersion was 10.19.

EXAMPLE 2

A coating composition of the present invention was prepared inaccordance with Example 1, except that the total solids content of thefinal composition (including PVOH) was 25%. The pH of the finaldispersion was 9.43.

Comparative Example 2A

A coating composition having only one type of population of silicaparticles was prepared in accordance with Comparative Example 1A, exceptthat the total solids content of the final composition (including PVOH)was 25%. The pH of the final dispersion was 10.34.

EXAMPLE 3

This example illustrates the preparation of a coating composition of thepresent invention. An initial aqueous silica slurry containing 25%solids was prepared. The solids in the initial slurry contained twodistinct populations of silica particles, which were 80% by weight PTGfumed silica and 20% by weight LUDOX™ colloidal silica. (See Example 1for a description of PTG fumed silica and LUDOX™ colloidal silica.)

A PVOH solution (prepared at 30% solids) was added to the initial silicaslurry at low agitation until the ratio of silica to PVOH was 5:1 byweight. A 3.0% solution of carboxymethyl cellulose (CMC), a thickener,was adjusted to pH 11.5 and was then added to the dispersion until adesired viscosity was attained. The amount of dry CMC relative to thetotal dry solids was 3.0% by weight. The total solids content of thecomposition was measured and water was added, if needed, until theresulting dispersion had a total solids content (including PVOH and CMC)of 20% by weight. The pH of the final dispersion was 10.40. Thus formedwas a coating composition of the present invention.

Comparative Example 3A

This example illustrates the preparation of a coating composition havingonly one type of population of silica particles. An initial aqueoussilica slurry of 30% solids content containing only PTG fumed silica(see Example 1) was prepared. A PVOH solution (prepared at 30% solids)was added to the initial silica slurry at low agitation until the ratioof silica to PVOH was 5:1 by weight. A 3.0% solution of carboxymethylcellulose (CMC), a thickener (pre-adjusted to pH 11.5) was then added tothe dispersion until a desired viscosity was attained. The amount of dryCMC relative to the total dry solids was 2.3% by weight. The solidscontent of the composition was measured and water was added, if needed,until the resulting dispersion had a total solids content (includingPVOH and CMC) of 20% by weight. The pH of the final dispersion was11.15.

EXAMPLE 4

A coating composition was prepared in accordance with Example 3, exceptthe amount of dry CMC relative to the total dry solids was 2.3% byweight. The total solids content of the composition (including PVOH andCMC) was 20% by weight. The pH of the final composition was 9.80.

Comparative Example 4A

A coating composition was prepared in accordance with ComparativeExample 3A, except the pH of the final composition was 10.17.

EXAMPLE 5

This example illustrates the improved rheological properties of acoating composition of the present invention. The viscosities of thecoating compositions prepared in accordance with Examples 1 and 2, andComparative Examples 1A and 2A, were measured under relatively low shearconditions and under relatively high shear conditions. Low shearviscosity was measured using a Brookfield Model RV viscometer(manufactured by Brookfield Engineering Laboratories, Inc., Stoughton,Mass.) at 100 RPM, spindle #4, after 30 seconds. High shear viscositywas measured using a HERCULES® High-Shear Viscometer at 4400 RPM (Bob:FF measuring geometry). All viscosities were measured at about 22° C.The results are shown in Table 1.

TABLE 1 Apparent Viscosity Apparent Viscosity Solids at Low Shear atHigh Shear Composition Content (centipoise) (centipoise) Example 1 20%30 13.1 Example 1A 20% 40 16.3 Example 2 25% 60 33.5 Example 2A 25% 7644.9

Rheograms were generated for the compositions of Examples 1, 1A, 2, and2A using a HERCULES® High-Shear Viscometer from 0-4400 RPM (Bob: FFmeasuring geometry, spring: 250). The rheograms are shown in FIG. 1. Therheograms generated by the compositions of the present invention(Examples 1 and 2) are designated 1 and 2 in FIG. 1, respectively. Therheograms generated by the compositions of Comparative Examples 1A and2A are designated 1A and 2A in FIG. 1, respectively.

These data demonstrate that the coating composition of the presentinvention has improved rheological properties over an analogouscomposition having only one type of particle population. The coatingcomposition of the present invention (Examples 1 and 2) exhibitedexcellent sheer thinning, which is desirable for high speedapplications. Moreover, the compositions of Examples 1 and 2 have lowerabsolute viscosities than analogous compositions employing only one typeof particle population (Comparative Examples 1A and 2A, respectively),as indicated by differences in their rheograms (see FIG. 1: 1 vs. 1A,and 2 vs. 2A).

EXAMPLE 6

This example illustrates the rheological properties of a coatingcomposition of the present invention for which a thickener is includedin the composition. The low shear and high shear viscosities of thecoating compositions prepared in accordance with Examples 3 and 4, andComparative Example 3A were measured in accordance with Example 5. Theresults are shown in Table 2.

TABLE 2 CMC Apparent Apparent relative Viscosity at Viscosity at tototal Solids Low Shear High Shear Composition solids (%) Content(centipoise) (centipoise) Example 3 3.0 20% 550 34.6 Example 3A 2.3 20%305 21.9 Example 4 2.3 20% 194 23.2

The higher viscosity of the composition of Example 3 relative to thecomposition of Comparative Example 3A is due to a higher concentrationof thickener. When the relative concentration of thickener is reduced,the low shear and high shear viscosities are reduced (see Example 4).The composition of the present invention (Examples 3 and 4) exhibitsgood shear thinning, as evidenced by the significant decrease inapparent viscosity at high shear rate. These data demonstrate that thecoating composition of the present invention exhibits desirablerheological properties, even in the presence of a thickener. The degreeof shear thinning, and relatively low apparent viscosity at high shearrate, demonstrate that the composition of the present inventionpossesses rheological properties that are desirable for high speedmanufacturing operations.

EXAMPLE 7

This example demonstrates the preparation of a glossy recording mediumof the present invention and demonstrates that the coating compositionof the present invention can produce a high gloss recording medium underhigh speed coating conditions. The coating compositions of Example 3 andComparative Example 3A were tested using a CLC (Cylindrical LaboratoryCoater) blade coating apparatus at high speed. The CLC simulatesconditions that are characteristic of commercial manufacture. Theperformance of a particular coating composition in the CLC at high speedis indicative of how the coating composition is expected to performunder high speed commercial manufacturing conditions.

Using the CLC, one side of a cellulose paper substrate was coated withthe compositions of Example 3 and Comparative Example 3A, at a rate of3000 feet per minute (914 meters per minute), dried (infrared). The drycoat weight in grams per square meter (g/m²) for each recording medium(i.e., coated substrate) was determined, and the dry recording media(uncalendered) were analyzed. Optical and surface properties weremeasured for each recording medium and also for the uncoated substrate.PPS (Parker Print Surf) roughness and brightness were measured.Brightness was measured in accordance with TAPPI brightness standard.Glossiness was measured in terms of the 75° specular gloss according toJIS P 8142 using a gloss photometer.

The recording media were calendered, and the 75° specular glossmeasurements were determined for the calendered media. The results areshown in Table 3. In Table 3, the recording medium of the presentinvention (i.e., coated with the coating composition of Example 3) isrepresented by “3,” and the recording medium coated with the coatingcomposition of Comparative Example 3A is represented by “3A.” The PPSporosity (ave.) of the uncoated substrate was 128.90.

TABLE 3 75° Specular PPS Coat Brightness Gloss Roughness Wt. (%) (%)(μm) Medium (g/m²) Ave. S.D. [Calendered] Ave. S.D. UNCOATED 0 90.380.26 7.20 [N/A] 4.58 0.08 3 7.95 91.37 0.24 17.2 [51.50] 4.11 0.09 3A8.66 89.60 1.17 13.33 [47.20] 4.37 0.31

These data demonstrate that the coating composition of the presentinvention exhibits excellent performance at high speed, producing aglossy recording medium with excellent optical and surface propertiesunder such conditions. These data confirm the experimental evidence thatthe composition of the present invention possesses rheologicalproperties desirable for high speed manufacturing operations.

The recording medium of the present invention (Example 3) has improvedoptical and surface properties over an analogous medium that containsonly one type of particle population in the coating (Comparable Example3A). The surface of the recording medium of the present invention ofExample 3 is brighter and glossier than the recording medium ofComparative Example 3A, as indicated by the higher values for brightnessand gloss. Moreover, the recording medium of the present invention ofExample 3 has a lower PPS roughness than the recording medium ofComparative Example 3A. As such, the recording medium of the presentinvention of Example 3 exhibited a smoother surface. Even aftercalendering, the recording medium of Example 3 demonstrated improvedglossiness over the recording medium Comparative Example 3A.

The recording medium of the present invention (Example 3) alsodemonstrated good liquid absorptivity, as indicated in FIG. 2. Thecontact angle exhibited a sharp initial decrease over the first twominutes, indicating good liquid absorptivity with respect to therecording medium of Example 3. The initial decrease in contact angleover time, as well as the overall observed absorptivity profile, wascomparable to the absorptivity profile observed for the recording mediumof Comparable Example 3A.

EXAMPLE 8

This example illustrates the preparation of a recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or a polymeric film with a coating composition having thecomposition recited in Table 4 to provide a coated substrate. The coatedsubstrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 4 Mean Material Diameter Amount First Group Pyrogenic silica 170nm  20 parts by weight Second Group Colloidal silica  35 nm  50 parts byweight Carrier (with binder) water (pH 9) 130 parts by weight

The apparent viscosity of the coating composition is calculated from thehigh shear rheogram of the composition using any suitable method.

The glossiness, packing density, pick strength, rate of liquidabsorption, liquid absorption capacity, and crack resistance of thecalendered recording medium are measured as previously described. Allmeasurements are performed on the side of the substrate having theglossy coating thereon. The crack resistance is measured by visuallyjudging the degree of cracking of the glossy coating after drying, andcharacterizing the cracking degree as: (a) substantially no cracksvisually evident, (b) few cracks visually evident, (c) moderatelycracked, or (d) extensively cracked.

EXAMPLE 9

This example illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or a polymeric film with a coating composition having thecomposition recited in Table 5 to provide a coated substrate. The coatedsubstrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 5 Mean Material Diameter Amount First Group Pyrogenic 170 nm  80parts by silica weight Second Group Colloidal  35 nm  50 parts by silicaweight Carrier water (pH 9) 370 parts by (with weight binder)

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

EXAMPLE 10

This ex ample illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or a polymeric film with a coating composition having thecomposition recited in Table 6 to provide a coated substrate. The coatedsubstrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 6 Mean Material Diameter Amount First Group Pyrogenic 170 nm  20parts by silica weight Second Group Colloidal  35 nm  50 parts byPortion 1 silica weight Second Group Monodispersed  55 nm  20 parts byPortion 2 polystyrene weight latex beads Carrier water (pH.9) 130 partsby (with weight binder)

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

EXAMPLE 11

This example illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or a polymeric film with a coating composition having thecomposition recited in Table 7 to provide a coated substrate. The coatedsubstrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 7 Mean Material Diameter Amount First Group Pyrogenic 170 nm  20parts by silica weight Second Group Colloidal  35 nm  50 parts byPortion 1 silica weight Second Group Monodispersed  50 nm  20 parts byPortion 2 polystyrene weight latex beads Carrier water (pH 9) 130 partsby weight Binder Polyvinyl  20 parts by alcohol weight

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

EXAMPLE 12

This example illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or polymeric film with a coating composition having thecomposition recited in Table 8 to provide a coated substrate. The coatedsubstrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 8 Mean Material Diameter Amount First Group Pyrogenic 170 nm  20parts by silica weight Second Group Colloidal  35 nm  50 parts byPortion 1 silica weight Second Group Monodispersed  50 nm  20 parts byPortion 2 polystyrene weight latex beads Second Group Monodispersed  20nm  10 parts by Portion 3 polystyrene weight latex beads Carrier water(pH 9) 130 parts by weight Binder Polyvinyl  25 parts by alcohol weightOther Brighteners,  1 part each Additives surfactants by weight

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

EXAMPLE 13

This example illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or a polymeric film with a coating composition having thecomposition recited in Table 9 to provide a coated substrate. The coatedsubstrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 9 Mean Material Diameter Amount First Group finely milled 170 nm 80 parts by silica weight Second Group Colloidal  35 nm  50 parts bysilica weight Carrier water (pH 9) 370 parts by weight

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

EXAMPLE 14

This example illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or a polymeric film with a coating composition having thecomposition recited in Table 10 to provide a coated substrate. Thecoated substrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 10 Mean Material Diameter Amount First Group Pyrogenic 170 nm  20parts by alumina weight Second Group Colloidal  35 nm  50 parts byPortion 1 silica weight Second Group monodispersed  55 nm  20 parts byPortion 2 polystyrene weight latex beads Carrier water (pH 9) 130 partsby (with binder) weight

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

EXAMPLE 15

This example illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or a polymeric film with a coating composition having thecomposition recited in Table 11 to provide a coated substrate. Thecoated substrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 11 Mean Material Diameter Amount First Group Pyrogenic 170 nm  20parts by alumina weight Second Group Colloidal  35 nm  50 parts byPortion 1 silica weight Second Group Monodispersed  50 nm  20 parts byPortion 2 polystyrene weight latex beads Carrier water (pH 9) 130 partsby weight Binder Polyvinyl  20 parts by alcohol weight

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

EXAMPLE 16

This example illustrates the preparation of the recording medium andcoating composition of the present invention.

An air-knife coater is used to coat one side of a cellulose papersubstrate or polymeric film with a coating composition having thecomposition recited in Table 12 to provide a coated substrate. Thecoated substrate is then dried to form a recording medium comprising asubstrate having a glossy coating thereon at a coverage on a dry basisof about 15 g/m². The recording medium is then calendered to enhancegloss.

TABLE 12 Mean Material Diameter Amount First Group Pyrogenic 170 nm  20parts by alumina weight Second Group Colloidal  35 nm  50 parts byPortion 1 silica weight Second Group Monodispersed  50 nm  20 parts byPortion 2 polystyrene weight latex beads Second Group Monodispersed  20nm  10 parts by Portion 3 polystyrene weight latex beads Carrier water(pH 9) 130 parts by weight Binder Polyvinyl  25 parts by alcohol weightOther Brighteners,  1 part each Additives surfactants by weight

The apparent viscosity of the coating composition, and the glossiness,packing density, pick strength, rate of liquid absorption, liquidabsorption capacity, and crack resistance of the calendered recordingmedium are measured as in Example 8.

All of the references cited herein, including patents, patentapplications, and publications, are hereby incorporated in theirentireties by reference.

While this invention has been described with an emphasis upon preferredembodiments, it will be obvious to those of ordinary skill in the artthat variations of the preferred embodiments may be used and that it isintended that the invention may be practiced otherwise than asspecifically described herein. Accordingly, this invention includes allmodifications encompassed within the spirit and scope of the inventionas defined by the following claims.

What is claimed is:
 1. A coating composition having a solids content ofat least about 15% by weight, and an apparent viscosity, when measuredat 4400 RPM, of less than about 100 centipoise at about 22° C.,comprising a carrier, a binder, and first and second groups ofparticles, wherein: (a) said first group comprises metal oxideparticles, wherein said metal oxide particles are aggregates of smaller,primary particles, (b) the mean diameter of said primary particles isless than about 100 nm, (c) the mean diameter of said aggregates is fromabout 100 nm to about 500 nm, (d) the mean diameter of the particles insaid second group is less than about 50% of the mean diameter of theaggregates in said first group, and (e) the ratio of particles in saidfirst group to particles in said second group is from about 0.1:1 toabout 10:1 by weight.
 2. The composition of claim 1, wherein the solidscontent of said composition is at least about 20% by weight.
 3. Thecomposition of claim 1, wherein said apparent viscosity is less thanabout 50 centipoise at about 22° C.
 4. The composition of claim 1,wherein the mean diameter of said aggregates is from about 100 nm toabout 300 nm.
 5. The composition of claim 1, wherein the ratio of saidfirst group of particles to said second group of particles is from about1.5:1 to about 8:1 by weight.
 6. The composition of claim 1, whereinsaid metal oxide is selected from the group consisting of silica,alumina, titania, zirconia, ceria, and magnesia.
 7. The composition ofclaim 6, wherein said metal oxide comprises silica.
 8. The compositionof claim 1, wherein said first group of particles are pyrogenic metaloxide particles.
 9. The composition of claim 1, wherein said secondgroup comprises particles of a material selected from the groupconsisting of metal oxides and synthetic polymers.
 10. The compositionof claim 9, wherein said second group comprises particles of silica. 11.The composition of claim 10, wherein said second group comprisesparticles of colloidal silica.
 12. The composition of claim 9, whereinsaid second group comprises particles of polystyrene.
 13. Thecomposition of claim 1, wherein said second group comprises particleshaving a mean diameter of less than about 100 nm.
 14. The composition ofclaim 1, wherein said second group comprises monodispersed particles.15. The composition of claim 1, wherein said second group comprises twoor more portions of particles, wherein each of said portions accountsfor at least about 1% by weight of the total particles in said secondgroup.
 16. The composition of claim 15, wherein one or more of saidportions comprises monodispersed particles.
 17. The composition of claim1, wherein said first group comprises particles of a cationic metaloxide.
 18. The composition of claim 1, wherein said second groupcomprises cationic particles.
 19. The composition of claim 1, whereinsubstantially all of the particles in the second group have diameters ofless than about 50% of the mean diameter of the aggregates in the firstgroup.
 20. The composition of claim 19, wherein substantially all of theparticles in the second group have diameters of less than about 50% ofthe diameters of substantially all of the aggregates in the first group.